Coupling assembly for stressing tendons of multi-span concrete structures

ABSTRACT

A coupling assembly for use in stressing multi-span posttentioned concrete structures, comprising a coupling device in which opposite ends of the stressing wires or strands of two adjacent sections of the stressing tendon are anchored, wherein co-operating cone-shaped elements are operatively associated with said coupling device and with one another to cause said wires or strands of one of said tendon sections to follow an S-shaped path.

United States Patent Surr Sept. 30, 1975 [5 COUPLING ASSEMBLY FORSTRESSING 3450.829 6/1963 Paul 24/122,.6

TENDONS 0F MULTl-SPAN CONCRETE 31775311 12 Surekar 2 STRUCTURES3.795.949 3/1974 Shorter 254/..9 A [75] Inventor: Eric Thornton Surr,Woodlesford, FOREIGN PATENTS OR APPLICATIONS E l d 1,452,219 8/1966France 52/230 892,133 3/1944 France 24/1226 1g CCL Systems Limited,surbltont 1,117,114 6/1968 United Kingdom 52/230 England 1.125.1768/1968 United Kingdom 52/230 [22] Filed: Nov. 16, 1973 PrimaryErammer-Bernard A. Gelak 1 PP N95 4161637 Attorney, Agent, orFirm-Baldwin, Wight & Brown [30] Foreign Application Priority Data [57]ABSTRACT 1 1972 United Kingdom 515070/72 A couplin'g assembly for use instressing multi-span post-tentioned concrete structures, comprising acou- 1 403/41; 24/1225; 403/364 pling device in which opposite ends ofthe stressing 1111- (31-2 F16G wires or strands of two adjacent sectionsof the stress- 1 1 Field Search 24/122-6' 115 R; 403/41; ing tendon areanchored, wherein co-operating cone- 52/2301 254/29 A shaped elementsare operatively associated with said coupling device and with oneanother to cause said 1 References Cited wires or strands of one of saidtendon sections to fol- UNITED STATES PATENTS low an S-shaped path.

3.405.490 10/1968 La Marr 52/230 3.449,876 6/1969 Howlett 52/230 9Claims 3 Drawing Figures g 2 g-x 1 6 r7 r. 22

J 6 fef US. Patent Sept. 30,1975 Sheet 1 of2 3,909,142

Sept. 30,1975 Sheet 2 of 2 3,909,142

US. Patent COUPLING ASSEMBLY FOR STRESSING TENDONS OF MULTl-SPANCONCRETE STRUCTURES This invention relates to a coupling assembly forthe stressing tendons of continuous mum-span posttensioned concretestructures. 1

In continuous multi-span concrete structure's a continuous tendonconsisting of a plurality of strands or wires is made up in sections,the strands or wires of each section being coupled or connected togetherby mechanical means. One such means comprises a coupling bar or atubular sleeve where all the strands or wires of the tendon are to betens'ioned simultaneously, or coupling sleeves for each strand or wirewhere the' strands or wires of the tendonare to be stressedindividuallyf Another means is that disclosed in our prior British Pat.No. 1,288,343 and its Patent of Addition No. 1,335,895, wherein acoupling device is formed witha plurality of central apertures toreceive and anchor one end of the wires or strands of one sectionof atendon,

' and with a corresponding number of peripheral slots to receive andanchor one end of the wires or strands of an adjacent section of thetendon.

In using the aforementioned coupling device, after having anchored theends of the wires or strands of one section in the centralapertures,'the endsof the wires or strands of the next adjacent sectionin the peripheral slots and are enclosed by a tapered grout box thesmaller end of which is the same, or substantially the same, size asthat of the main duct through which the tendon extends. Thus. when thewires orstrands are tensioned, it will be appreciated that they extendin a straight line between their anchorage pointsand the points at whichthey change direction on entering the main duct. I

Due to the fact that there is a limit to which any given size wire orstrand can be bent to assemble-the anchorage, and a limit to which thatwire or strand can be bent, particularly at the point where it leavesits anchorage, .during ultimate tensile load testing thereof withoutbreaking at that point; the grout box must be relatively long. I I

Thus, it will be appreciated that the use of such an assembly results inlarge voids being created in the concrete structure which has thedisadvantage that the structure, in the vicinity of the couplingassembly, has to be of increased size. This disadvantage is particularlynoticeable in structures such as bridge beams where the increase in sizeoccurs in the vicinity of the piers.

It is among the objects of the present invention to provide a couplingassembly which avoids, or substantially reduces, the aforementioneddisadvantage.

According to the present inventiomthere is provided a coupling assemblyfor the stressing tendons of multispan post-tensioned concretestructures, comprising a coupling device having centrally'disposedaxiallyextending means for anchoring one end of the wires or strands ofone section of the stressing tendon, and other means formed on theperiphery thereof for anchoring one end of the wires or strands of anadjacent section of the stressing tendon, a'wireor strand deflectorattached to the coupling device to extend in the same general directionas the wires or strands'of said adja cent section of the stressingtendon, and a reducing ele device to extend in the same general directionas the wire or strand deflector, the arrangement being such that, inuse, the wires or strands of said adjacent section ment attached to theouter periphery of the coupling are disposed between the deflector andthe reducing element.

The deflector and the reducing element are both preferably offrusto-conical formation and the shapes thereof are such that theexternal surface of the deflector and the internal surface of thereducing element determine the bending angle of the wires or strands.

The invention is illustrated by way of example in the accompanyingdrawings in which,

FIG. 1 is a longitudinal section through a coupling assembly accordingto the invention,

FIG. 2 is a section on the line 22 of FIG. I, and

FIG. 3 is a section corresponding to part of FIG. 1 showing amodification.

Referring to FIGS. 1 and 2 of the drawings, there is shown a couplingassembly comprising a coupling de vice 1 consisting of an annularbearing plate 2 formed with an integral flange 3, and a disc-likebearing plate 4 positioned over the bore 5 of the annular bearing plate2 to engage one face of the latter.

A plurality of transverse bores 6 of conical formation, the number ofwhich varies according to the size of the tendon to bejoined, areprovided to extend through the plate 4 and are each adapted, in use, toreceive a wire or strand, indicated at S, of one section of the tendon.

The bores 6 are each formed to receive, in addition to the wire orstrand S, a wedge device 7 by which the wire or strand is anchored inthe bearing plate. The wedge devices 7 are of known construction andeach comprise two or more arcuate wedge elements which are positionedbetween the bore 6 and the wire or strands.

The peripheral edge of the flange 3 of the bearing plate 2 is formedwith a plurality of transverse recesses or grooves 8 which are of awidth to receive a single wire or strand, indicated at S, of the nextadjacent section of the tendon. The number of grooves or recesses 8correspond to the number of bores 6 and will of course vary with thenumber of wires or strands in the tendon.

The ends of the strands S extend through the bores 6 and are anchored inthe bores, as hereinbefore described, by the wedge devices 7. Thestrands S' however are held in position in the grooves or recesses 8 bymeans of anchoring fittings 9 which are secured to the ends of thestrands.

The anchoring fittings 9 may each comprise a compression fitting ofknown construction consisting of a cylindrical sleeve one end of whichis formed with an inwardly directed annular flange, and an insertreceived in the sleeve, the insert being provided with at least twolongitudinally disposed slots and being knurled or otherwise roughened,both internally and externally, to increase friction between the insertand the wire or strand. After positioning the sleeve is compressed ontothe wire or strand to provide a permanent fitting.

An alternative form of anchoring fitting 9 may comprise a so-calledbarrel and wedge type fitting consisting of a cylindrical barrel havinga frusto-conical bore to receive a wire or strand and a plurality ofwedge elements which grip and anchor the wire or strand in the barrelthereby providing an end fitting which can, if necessary, be removedfrom the wire or strand.

To ensure against any tendency for the anchoring fittings 9, which arepreferably of a metal having a relatively low shear value compared withthat of the coupling device 1, from shearing through the open grooves orrecesses 8 when the strands S are under tension, a hard metal washer ispositioned between each fitting 9 and the face of the bearing plateflange 3. The washers 10 are passed over the ends of the strands beforethe fittings 9 are fixed thereon.

The coupling assembly further comprises a wire or strand deflector 11 ofgenerally frusto-conical formation. The deflector 11 is preferably ofcast iron and is supported at one end by being fitted over the plate 4.The sizes of the plate 4 and the deflector 11 are such that the portionsof the strands S in the vicinity of the coupling device I extendparallel to the axis of the assembly and are not therefore subjected tobending at the points where they leave their co-acting anchoringfittings 9 which are also disposed parallel to the axis of the assembly.

That portion of the deflector 11 away from the coupling device 1 isarcuately tapered to present a support surface which corresponds to thepermissable bending angle of the strands S, the angle depending on thediameter of the strands.

Surrounding the strands S is a reducing element 12 of generallyfrusto-conical formation. The wide end of the element 12 is positionedover the coupling device 1 and the narrow end thereof is arcuatelytapered, in the opposite sense to that of the deflector 1 l, to presenta surface which corresponds to the permissable bending angle of thestrands S. The extreme narrow end of the element 12 corresponds to thesize of the main duct of the structure through which the tendon passes.Thus, it will be seen that the assembly is such that the strands S arenot subjected to bending at the point where they leave their anchoringfittings 9, or at the points where they enter the main duct.Furthermore, at a position between the aforementioned points, they arebent in two opposite directions to present an S formation to an extentwhich does not exceed the permissable amount.

The deflector 11 has the particular advantage that it serves todistribute the load transmitted from the strands S back into theprevious span of the structure, and the S formation imparted to thestrands S has the advantage that it reduces the length of the wholeassembly compared with the prior art assemblies, and thus reduces thesize of the voids in the structure.

The reducing element 12 is provided with a grout pipe 13 and ispreferably formed of a synthetic plastics glass fibre reinforcedmaterial. However, and other suitable materials such as metal may beused provided only that the element is sufficiently rigid to withstandthe pressure of the concrete which is poured over it to form thestructure prior to the tensioning of the strands S.

In building a concrete structure, the first span of the structure, whichis partly indicated at 14, terminates at the coupling point in aconventional tube unit 15 which is cast into the concrete, and which isconnected by conventional ducting to a further tube unit cast into theconcrete at the other end of the structure.

Strands S are then threaded through the ducting, the

bore 5 of the plate 2, and the bores 6 of the bearing plate 4, theopposite ends of the strands being anchored at the other end of thestructure. The bearing plate 4 is then temporarily attached to thetubeunit 15 by means of bolts (not shown) which are positioned in lugs 16provided on the plate 2.

The strands S are then tensioned either individually or collectively andanchored in position by the wedge devices 7.

The bolts holding the coupling device are then released and, using thesame bolts, a grouting cover is positioned over the projecting ends ofthe anchored strands to form a sealed cavity around the wedge devices.Grout is then injected into the grout cover and flows, via grout holes(not shown) into the ducting whereby the tendon is grouted in the normalmanner. The grout cover is then removed leaving a covering of groutindicated at 17, the coupling device being held in position against thetube unit 15 of the structure with the bearing plate 4 spaced from thestructure bythe bearing plate 2.

The construction of the next section of span of the structure, and thusof the tendon, is now commenced. Firstly, the deflector 11 is placed inposition. The reducing element is threaded over the. ends of the strandsand the anchoring fittings 9 and washers 10 are then applied to one endof each of the strands S. and the other ends of the strands are threadedthrough the main ducting of said next section or span. The strandscomplete with the fittings 9 are then placed around the deflector 11 andthe fittings 9 are placed in their respective slots to take up thepositions shown in the drawings. The strands are held in position bytape or other. binding and the reducing element 12 is then pushedaxially towards the anchorage thereby forcing the strands to adopt theS-shaped formation which occurs when the element 12 is in its finalposition as shown in the drawings.

In the latter respect, the angle of deviation of the strand, or theradii through which the strand bends should be approximately 15 to thehorizontal. The

maximum radius that can be utilised, is dependent on the force requiredto position the reducing element be fore stressing. It will beappreciated that this will be forced axially towards the anchorage andit should be possible for two men to finally position the reducingelement with the use of excessive force. On examination it will be notedthat different sizes of strand diameter and construction are used inpre-stressed concrete anchorages, because of this, the number of strandsin any anchorage will vary and therefore the geometric determination ofthe angle forming the S configuration must be a compromise between themaximum S configuration, giving maximum reduction in length, and minimumS configuration giving greatest ease of assembly.

With the parts in the aforementioned position, the concrete is pouredinto the second section of the structure thus covering the element 12enclosing the coupling device. At a suitable time, the second section ofthe tendon is tensioned and subsequently grouted in the same manner asthat hereinbefore described, the load in this case being taken by thefittings 9 and transmitted by the first section coupling device to thefirst section of the tendon.

Thus, it will be appreciated that any number of concrete sections orspans can be added on the same principle as that hereinbefore described.

In the modified arrangement shown in FIG. 3, the coupling device 1 isprovided as a single block element which is cut away at 18 to receivethe deflector 1 l. The block may be solid or it may be formed with arecess as indicated by dot dash lines 19. In other respects, theassembly of this embodiment is constructionally and operationally thesame as that described with reference to FIGS. 1 and 2.

Although the deflector 11 has been described as being of cast iron, itwill be understood that the invention is not limited in this respect.Thus, the deflector may be of pre-cast concrete or any other materialhaving sufficient strength to withstand the inward radial pressureapplied thereto.

1 claim:

1. A coupling assembly for the stressing of multi-span post-tensionedconcrete structures, comprising a coupling device having centrallydisposed axially extending means for anchoring one end of strands of onesection of a stressing tendon in a first direction, and other meansformed on and about the periphery of said coupling device for anchoringone end of strands of an adjacent section of said stressing tendon in anopposite direction, a strand deflector operatively associated with saidcoupling device and extending beyond said coupling device in the samegeneral direction as said strands of said adjacent section of saidstressing tendon, said strand deflector extending generally from saidother anchoring means and sloping radially inwardly therefrom, and areducing element fitted over said coupling device adjacent said otheranchoring means and extending beyond said coupling device in the samedirection as that of said deflector, said deflector having a portionadjacent said coupling device generally corresponding in outline toadjacent portions of said reducing element whereby strands of saidadjacent section adapted to lie between and axially of said deflectorand said reducing element will be shaped by said deflector and saidreducing element.

2. An assembly as claimed in claim 1, in which said deflector isgenerally in the form of a truncated cone, said deflector having aportion adjacent said coupling device lying substantially parallel withthe axis of the assembly and the remainder of said deflector being ofconvex tapered formation.

3. An assembly as claimed in claim 2, in which said reducing element isgenerally in the form of a truncated cone, a portion of said reducingelement being of concave tapered formation being cooperable with saidconvex portion of said deflector to react on said strands of saidadjacent section to constrain the same to follow an S-shaped path.

4. A coupling assembly for the stressing of multi-span post-tensionedconcrete structures, said coupling assembly comprising an annularcoupling device having a bore, said device having centrally disposedaxially extending anchorage means for anchoring one end of strands ofone section of a stressing tendon, and other anchoring means formed onandabout the periphery of said annular coupling device for anchoring oneend of strands of an adjacent section of said stressing tendon, a stranddeflector of truncated cone shape attached at one end to said couplingdevice and extending beyond said coupling device in the same generaldirection as said strands of said adjacent section of said stressingtendon, said deflector having a portion adjacent said coupling devicelying substantially parallel with the axis of the assembly and theremainder of said deflector being of convex tapered formation, areducing element of truncated cone shape fitted at one end over saidcoupling device and extending beyond said coupling device in the samedirection as that of said deflector, said reducing element having aportion of concave tapered formation, strands of said adjacent sectionbeing adapted to extend between and axially of said deflector and saidreducing element with said convex portion of said deflection and saidconcave tapered portion of said reducing element being cooperable toreset strands of said adjacent section to constrain the same to follow agenerally S-shaped path adjacent said coupling device.

5. An assembly as claimed in claim 4, in which said coupling devicecomprises a single metal block.

6. An assembly as claimed in claim 4, in which said coupling devicecomprises an annular bearing plate and a co-acting disc-like bearingplate positioned over the bore of said annular bearing plate.

7. An assembly as claimed in claim 4, in which said centrally disposedanchorage means comprise a plurality of tapered holes formed in saidcoupling device, said tapered holes being formed to receive said strandsand retaining wedges which anchor said strands in said holes.

8. An assembly as claimed in claim 7, in which the said other anchoringmeans comprise a plurality of circumferentially spaced axially disposedrecesses formed in the periphery of said coupling device.

9. An assembly as claimed in claim 8, in which said strands are anchoredin said recesses by means of anchoring fittings attached to saidstrands, said anchoring fittings, in use, lying parallel to the axis ofthe assembly.

1. A coupling assembly for the stressing of multi-span posttensionedconcrete structures, comprising a coupling device having centrallydisposed axially extending means for anchoring one end of strands of onesection of a stressing tendon in a first direction, and other meansformed on and about the periphery of said coupling device for anchoringone end of strands of an adjacent section of said stressing tendon in anopposite direction, a strand deflector operatively associated with saidcoupling device and extending beyond said coupling device in the samegeneral direction as said strands of said adjacent section of saidstressing tendon, said strand deflector extendIng generally from saidother anchoring means and sloping radially inwardly therefrom, and areducing element fitted over said coupling device adjacent said otheranchoring means and extending beyond said coupling device in the samedirection as that of said deflector, said deflector having a portionadjacent said coupling device generally corresponding in outline toadjacent portions of said reducing element whereby strands of saidadjacent section adapted to lie between and axially of said deflectorand said reducing element will be shaped by said deflector and saidreducing element.
 2. An assembly as claimed in claim 1, in which saiddeflector is generally in the form of a truncated cone, said deflectorhaving a portion adjacent said coupling device lying substantiallyparallel with the axis of the assembly and the remainder of saiddeflector being of convex tapered formation.
 3. An assembly as claimedin claim 2, in which said reducing element is generally in the form of atruncated cone, a portion of said reducing element being of concavetapered formation being cooperable with said convex portion of saiddeflector to react on said strands of said adjacent section to constrainthe same to follow an S-shaped path.
 4. A coupling assembly for thestressing of multi-span post-tensioned concrete structures, saidcoupling assembly comprising an annular coupling device having a bore,said device having centrally disposed axially extending anchorage meansfor anchoring one end of strands of one section of a stressing tendon,and other anchoring means formed on and about the periphery of saidannular coupling device for anchoring one end of strands of an adjacentsection of said stressing tendon, a strand deflector of truncated coneshape attached at one end to said coupling device and extending beyondsaid coupling device in the same general direction as said strands ofsaid adjacent section of said stressing tendon, said deflector having aportion adjacent said coupling device lying substantially parallel withthe axis of the assembly and the remainder of said deflector being ofconvex tapered formation, a reducing element of truncated cone shapefitted at one end over said coupling device and extending beyond saidcoupling device in the same direction as that of said deflector, saidreducing element having a portion of concave tapered formation, strandsof said adjacent section being adapted to extend between and axially ofsaid deflector and said reducing element with said convex portion ofsaid deflection and said concave tapered portion of said reducingelement being cooperable to reset strands of said adjacent section toconstrain the same to follow a generally S-shaped path adjacent saidcoupling device.
 5. An assembly as claimed in claim 4, in which saidcoupling device comprises a single metal block.
 6. An assembly asclaimed in claim 4, in which said coupling device comprises an annularbearing plate and a co-acting disc-like bearing plate positioned overthe bore of said annular bearing plate.
 7. An assembly as claimed inclaim 4, in which said centrally disposed anchorage means comprise aplurality of tapered holes formed in said coupling device, said taperedholes being formed to receive said strands and retaining wedges whichanchor said strands in said holes.
 8. An assembly as claimed in claim 7,in which the said other anchoring means comprise a plurality ofcircumferentially spaced axially disposed recesses formed in theperiphery of said coupling device.
 9. An assembly as claimed in claim 8,in which said strands are anchored in said recesses by means ofanchoring fittings attached to said strands, said anchoring fittings, inuse, lying parallel to the axis of the assembly.